Tetrahedrally coordinated half-metallic antiferromagnets

We explore the electronic structures of transition-metal-based chalcopyrites TMX2 (X=S, Se, and Te) to establish a concept of half-metallic antiferromagnets (HM-AFM's) within the class of tetrahedrally coordinated ternary systems. Using a full-potential muffin-tin approach and the spin-polarized density functional method, we find two series of HM-AFM's: CrFeX2 and VCoX2, where two constituent magnetic ions in a unit cell have antialigned local moments that cancel exactly by virtue of the integer filling of one spin channel. The bonding nature is interpreted in terms of the ghost-bond-orbital model; the T-X bonds are covalent while the M-X bonds are ionic, suggesting the magnetic interaction in each bond is due to ferromagnetic double exchange and antiferromagnetic superexchange, respectively, in the conventional scheme.